The high-pressure common-rail fuel injection system is one of the key technologies of diesel engines, which directly affects engine combustion. An energy storage chamber type common rail injector was studied in this paper. The injector is considered to have good control of pressure fluctuation by utilizing a special chamber inside its body. To investigate the flow and cavitation characteristics of the injector, a computational fluid dynamic model was built and validated by experimental data. The flow performance of the energy storage chamber, control valve, and SAC was conducted. The results show that the flow inside the energy storage cavity is smooth, and there is almost no cavitation phenomenon. Although the eccentric valve needle of the control valve will accelerate the flow rate, it will cause a serious cavitation phenomenon, which should be avoided. Increasing the diameter of the injector needle will weaken the cavitation, but it will cause the injector needle valve outlet flow rate to decrease. Finally, for the SAC cavity, increasing the cavity radius, increasing the nozzle inlet angle, and reducing the nozzle length can improve the discharge coefficient and optimize the flow characteristics of the injector.